1. Field of the Invention
The present invention relates to a mechanism in roll-up devices for safety belts in motor vehicles, where the safety belt which, addressed by one or more danger sensors, can be blocked via a belt shaft, is stressed in tension by a spring force in the winding-up direction of the belt shaft, and where, within a short range or rotation of the belt shaft in the pull direction of the safety belt, a locking device for the belt shaft, acting against the elastic winding-up spring force, is made effective by control gates of plate cams.
2. Description of the Prior Art
Safety belts which have an end held by a mechanism for rolling-up and holding the safety belt taut, are used for protecting passenger against injuries. Into this mechanism is built a device which is capable of blocking this mechanism and thereby, also the safety belt, in the event that an extreme acceleration or braking force, which normally occurs in accidents, acts through a built-in danger sensor on the motor vehicle or the motor vehicle passenger.
Safety belts applied as close to the body as possible lead to increased safety against accident injuries. For this reason, safety belt arrangements are equipped with a mechanism which pulls the safety belt against the body. This mechanism serves at the same time for rolling-up the safety belt as far as possible if the safety belt is taken off. As a result a loosely hanging safety belt which impedes persons entering or leaving the vehicle and leads to accidents is avoided.
To accomplish the rolling-up function for the safety belt in a satsifactory manner, an appropriate pulling force must be exerted on the safety belt. This is normally effected by a spring element arranged in the rolling-up mechanism. The force action exerted by the spring element propagates via the safety belt and affects the persons protected by the safety belt according to regulations in a disagreeable manner. A reduction of the pulling force by the roll-up mechanism would clearly have a more favorable effect on the person to be protected. Reducing the restoring forces for the safety belt by a corresponding amount, however, would also affect the pulling-back function adversely, usually to an excessive degree.
For this reason, it has become known (U.S. Pat. No. 3,834,646) to make available a sufficiently large pulling-back force for the safety belt as well as to take care that this pulling-back force is made ineffective at times. This is accomplished, for instance, via plate cams which act on a locking device. This locking device is capable of blocking the belt shaft at least against the rolling-up force if corresponding control criteria are fed-in via the plate cams. As a control criterion it is evaluated on what distance the safety belt has traveled from its last-occupied rest position by pulling it out against the restoring force. As a further criterion it is evaluated whether, for instance, the car door is open. The position of the door can be signaled to the control device of the locking mechanism via a flexible cable. An open door is evaluated to cause the locking device to be put out of action in any case, so that the safety belt is rolled up.